But as “First Class” roars to its final climatic scene, it appeals to an insidious suspension of disbelief; the heroic mutants of America, bravely opposing bigotry and fear, are revealed as not so much a spectrum of humankind, but as Eagle Scouts from Mayfield. Thus, “First Class” proves itself not merely an incredible film, but an incredible work of American historical fiction. Here is a period piece for our postracial times — in the era of Ella Baker and the Rev. Dr. Martin Luther King Jr., the most powerful adversaries of spectacular apartheid are a team of enlightened white dudes....